what is "but the header is of low capacity?" do you mean it's a small diameter?
As a quick answer, the flow will try to double thru' the discharge pipe, with the head loss increasing by the square of the flow- rate increase.
To make any real sense a lot more data is required, you need to describe the full system - advise the flowrate, head against the pump, static heads component - from this we can make a few assumptions.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
Data, to start with describe the system, is there 1 pump installed and you wish to add another, yes /no.
If 1 pump, flow rate, total static head, total head on the pump.
Is the second pump identical?
Pump curves would help
What I gave in 29th Aug post is sufficient to make some accurate predictions.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
pump specifications:
Max Rpm at full load:2948 RPM
Amp: 50 amperes
power: 30 kw
Q: 180 cubicmetres per hr
two such pumps are connected to inlet header and outlet header of the chillers evaporator. basically its a circulation loop.
my query is when i measure flow rate in the header by using ultrasonic flow meter its showing 170 cubicmetres per hr.
if i apply affinity laws i.e, each pump is running at 80% load, RPM becomes 0.8*2948=2356 RPM. since flow proportional to RPM for constant Impellor, Q=180*2356/2948=143.85 cubicmetres/hr. since they are connected in parallel flow should double i.e flow in the header should be 143.85*2=290 cubicmeters/hr.
Where you are going wrong is this.
When you run the two pumps in paralell you do not get double the flow but somewhat less. It does depend on the system but two pumps may only give a few percent more but 10-25% more would be typical.
I will use some made up numbers to demonstrate the point.
You have two identical pumps and they each pump when operating alone 100m3/hr at a head of 100metres. In my made up system at 100m3/hr the total head in the system is 100metres. At 110m3/hr the system head increases to 120m, at 130m3/hr the head increase to 150 m and at 200m3/hr the head is 400m.
We know that these standard pumps decrease in output as the head increases.
One pump is pumping 100m3/hr at 100m head when we start the second pump. The second pump at start up because it is in paralell immediately is working against 100m head but as it starts to pump the flow increase somewhat. Lets say the total flow is now 130m3hr in the system so the head is 150m. The flow has increased by 30% but the head has increased by 50%.
In this case if we looked at the pump curve we would find that at 100m head the pump will produce 100m3/hr but at 150 m head(which is what it sees at the discharge because the pumps are paralell connectted) it will only produce 65m3/hr which is half of the total flow of 130m3/hr. So whilst bringing the the second pump online increases the total flow the increase in flow also increases the total head which reduces the flow per pump.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
Don't take this as criticism, my suggestion is to do some reading on basic pump theory, there is enough available on the internet to keep you reading for ages.
Until such times you get the basics together there is no way you can make much sense of what you are asking.
For instance the affinity rules have nothing to do with motor / pump efficiency and speed in the manner you have presented here.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
I agree with Artisi. Your posts show that you do not understand even the very basic principles of pump design and flow mechanics. That's where you are going wrong.
Your figures are meaningless.
Please go and find someone in your company who can explain these things to you or go and find a pump fundamentals video on you tube and read up a bit on things like pump curves, friction losses etc or search a bit more on this forum
can you please explain the relation between rpm of the shaft and percentage of load at which motor is working. elaborating.... if my motor is working at 80% of full load what is my rpm of the shaft?
You need to look at and understand pump curves like the one below.
The pump speed is constant.
The pump flow will vary depending on the back pressure of the downstream system (pipe, chiller pressure drop etc). This will impact on the pump flow which tracks the particular line.
So in this example, if the impellor is 10.5 diam, the required head from the pump is say 400 ft, then the flow will be 1000 gpm and the power approx. 145bhp
If on the other hand the required head from the pump needs to be 450 ft to overcome the friction losses, then the flow reduces to 750 gpm and the power also reduces to approx. 120 bhp.
This is the same pump running at the same speed. This is how centrifugal pumps work.
Understand that issue before you move on.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
The system is connected with VFD(variable frequency drive) where shaft rpm can be changed.
I got clarity on what happens to the flow when identical pumps are connected in parallel.
